CHAPTER XX 

 SYNTHETIC CULTURE MEDIA 



H. W. SCHOENLEIN 

 Detroit, Mich. 



Synthetic culture media such as are used in the bacteriological laboratory may be 

 defined strictly as those substrates which contain only ingredients of known composi- 

 tion and purity, and prove useful in the cultivation of micro-organisms. In some 

 cases, the term is used more loosely to include certain media in which the ingredi- 

 ents are of known or specified purity, though not necessarily of known composition. 

 Occasionally the term is (incorrectly?) used for certain media containing materials 

 of unknown or indefinite composition.' 



Synthetic media may therefore be grouped under the following headings: 



A. Synthetic media in the strict sense 



B. Pseudo-synthetic media 



1. Media in which there are present compounds of more or less uncertain chemical com- 

 position, but of known purity. For example, the exact chemical composition of certain 

 of the proteins is unknown, although they may be secured in a condition of high purity. 

 In such media the materials of unknown composition are nutrients. 



2. Media in which all nutrients are of known composition, but in which the non-nutrients 

 may be of unknown or indefinite composition. Agar, for example, may be quite com- 

 pletely freed from materials which might serve as nutrients. Its exact chemical com- 

 position is somewhat indefinite, and it is not itself a nutrient for most micro-organisms. 

 Its inclusion in the medium is therefore frequently not regarded as preventing such a 

 medium being classed as synthetic. 



It is commonly agreed that a medium is non-synthetic if it includes plant or 

 animal extracts, digests, infusions, or tissues. 



In general, the media used by the earlier workers in bacteriology were non- 

 synthetic; most of the synthetic media have been suggested within the last three 

 decades. A few were noted as useful before 1900. Probably the first to be described 

 was that of Cohn.^ This investigator developed a synthetic medium containing 

 ammonium tartrate which he found to be particularly useful for the cultivation of 

 fluorescent bacteria. Other early synthetic media were proposed by Naegeli,^ Fermi,^ 

 Uschinsky,5 Beijerinck/ and Winogradsky.'' Synthetic media are listed by Krasnow, 



' The so-called Waksman's synthetic acid agar contains peptone, an indefinite mixture' of un- 

 known composition. 



^ Cohn, Ferdinand: Beitr. z. Biol. d. Pflanzen, i, 127. 1875. 



^Naegeli,: C. Untersuchungen iiber niedere Pilze aus dent Pflanzenphysiologischem Instihit in 

 Miinchen. 1882. 



■'Fermi, C: Arch.f. Hyg., 14, i. 1892. 



sUschinsky, N.: Cenlralbl.f. Bakteriol., I AbL, 14, 316. 1893. 



'^Beijerinck, M. W.: ibid., II Abt., i, i. 1895. ? Winogradsky, S.: ibid., II Abt., 2, 425. 1896. 



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